1. Field of the Invention
The present invention relates to a hydraulic lash adjuster for taking up clearance or lash in a valve train of an internal combustion engine.
2. Description of the Prior Art
Such a lash adjuster of the kind referred to is known and may be mounted either between an engine valve stem and a valve operating cam or between one end of a rocker and its operating cam. An example of a lash adjuster mounted between an engine valve stem and a valve operating cam is shown in FIG. 5.
Referring to FIG. 5, a lash adjuster includes a main body 1 slidably installed in engine cylinder head 2 at a place adjacent an intake valve 3. The main body 1 consists of an outer tubular member 5 having an upper end wall 4 and an inner tubular member 7 secured at a lower outward flange 6 thereof to the outer tubular member 5. A first reservoir 8 is defined between the inner and outer tubular members 7, 5 and is communicated through an oil inlet port 9 formed in the outer tubular member 5 with an oil supply port 10 formed in the cylinder head 2. A stationary plunger 11 is disposed in the inner tubular member 7 and secured at the upper end thereof to the end wall 4 of the outer tubular member 5. The stationary plunger 11 has within the inside thereof a second reservoir 13 in fluid communication with the above described first reservoir 8 through first communication ports 12 formed in the inner end thereof. A movable plunger 14 is movably disposed between the inner tubular member 7 and the stationary plunger 11. The movable plunger 14 has within the inside thereof a high pressure chamber 16 which is in fluid communication through a second communication port 15 formed in the lower end portion of the stationary plunger 11 with the second reservoir 13. Within the high pressure chamber 16 there is disposed a ball valve 18 which is uged by springs 17, 17' in the direction closing the second communication port 15.
With the above arrangement, when a valve operating cam 19 is engaged at its base circle with the upper end wall 4 of the outer tubular member 5, namely, prior to lifting by the operating cam 19, oil from the oil supply passage 10 is introduced through the inlet port 9, the first reservoir 8 and through the first communication ports 12 to the second reservoir 13. Oil is then supplied through the second communication port 15 and the ball valve 18 in an opened state to the high pressure chamber 16, thus causing the movable plunger 14 and the main body 1 to move away from each other, i.e., in the opposite directions for thereby eliminating clearance between the operating cam 19 and the valve 3. On the other hand, when the operating cam 19 is engaged at its cam lobe with the upper end of the outer tubular member 5, namely, upon lifting by the operating cam 19, pressurized oil in the high pressure chamber 16 urges the ball valve 18 against its seating, thus confining pressurized oil within the high pressure chamber 16 and causing the main body 1 and the movable plunger 14 to move downward as an integral unit.
A disadvantage of the prior art lash adjuster is that it cannot function properly when air bubbles are contained in the working oil, resulting in a noisy and unsmooth operation of an associated valve train.